Genetics

A new technology for studying the human body’s vast system for toggling genes on and off reveals that genes connected with the immune system switch on and off more frequently than other genes, and those same genes operate differently in women and men. What’s more, the differences in gene activity are mostly not genetic.

A couple of years ago, geneticists Howard Chang, MD, PhD; Will Greenleaf, PhD, and others at Stanford invented a way to map the epigenome – essentially the real time on/off status of each of the 22,000 genes in our cells, along with the switches that control whether each gene is on or off.

Imagine a fancy office vending machine that can dispense 22,000 different drinks and other food items. Some selections are forever pumping out product; other choices are semi permanently unavailable. Still others dispense espresso, a double espresso or hot tea depending on which buttons you push. The activity of the 22,000 genes that make up our genomes are regulated in much the same way.

That’s a lot to keep track of. But Chang and Greenleaf’s technology, called ATAC-seq, makes it almost easy to map all that gene activity in living people as they go about their lives. Their latest study, published in Cell Systems, showed that the genes that switch on and off differently from person to person are more likely to be associated with autoimmune diseases, and also that men and women use different switches for many immune system genes. That sex-based difference in activity might explain the much higher incidence of autoimmune diseases in women — diseases like multiple sclerosis, lupus and rheumatoid arthritis.

The team took ordinary blood samples from 12 healthy volunteers and extracted immune cells called T cells. T cells are easy to isolate from a standard blood test and an important component of the immune system. With T cells in hand, the team looked at how certain genes are switched on and off, and how that pattern varied from individual to individual. Chang’s team also looked at how much change occurred from one blood draw to the next in each volunteer.

Chang told me, “We were interested in exploring the landscape of gene regulation directly from live people and look at differences. We asked, ‘How different or similar are people?’ This is different from asking if they have the same genes.”

Even in identical twins, he said, one twin could have an autoimmune disease and the other could be perfectly well. And, indeed, the team reported that over a third of the variation in gene activity was not connected to a genetic difference, suggesting a strong role for the environment. “I would say the majority of the difference is likely from a nongenetic source,” he said.

Years ago, when I first learned that genetic testing could help screen for some cancers, such as breast, ovarian and bone, it seemed like a no-brainer to get this testing done. Now I know better; genetic testing is a helpful tool that can help you assess your risk for certain kinds of cancer, but it’s not recommended for everyone. Senior genetic counselor Kerry Kingham, a clinical assistant professor affiliated with the Cancer Genetics Clinic at Stanford, explains why this is the case in a recent Q&A with BeWell@Stanford.

Cancer can be “hereditary” or “sporadic” in nature, Kingham says. Hereditary cancers, such as the forms of breast cancer related to a mutation in the BRCA1 or BRCA2 genes, are associated with an inherited genetic mutation. In contrast, sporadic cancers arise independent of family history or other risk factors. Since genetics testing detects gene mutations, it can only be used to help screen for the mutations that may lead to forms ofhereditary cancer.

Kingham elaborates on this point, when it makes sense to get genetic testing, and what the results may mean in the Q&A:

Twelve percent of women in the U.S. develop breast cancer; it is a common disease. Yet, only five to ten percent of these women will develop breast cancer because of a hereditary gene mutation.

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The best step to take prior to deciding whether or not to proceed with genetic testing is to meet with a genetic counselor. Your doctor can provide a referral. The genetic counselor will take a three generation family history, discuss the testing that might be indicated for you or a family member, and explain the risks and benefits of the testing. They also discuss the potential outcomes of the testing: whether a mutation is found, a mutation is not found, or there are uncertain results. Even when a genetic test is negative, this may not mean that the individual or their family is not at risk for cancer.

At this point you may be wondering: Why bother with genetic testing if it’s only useful for hereditary cancers and a negative test result is no guarantee you’re risk-free? Kingham’s closing comment addresses this question nicely: “I would say that your genes don’t change – they are what they are, and knowing what is in our genes can often help us learn how to take better care of our health.”

Writing about pancreatic cancer always gives me a pang. My grandmother died from the disease over 30 years ago, but I still remember the anguish of her diagnosis and the years of chemotherapy and surgery she endured before her death. This disease is much more personal to me than many I cover.

Unfortunately, survival rates haven’t really budged since I was in high school, in part because the disease is often not diagnosed until it’s well established. As geneticist Monte Winslow, PhD, described to me in an email:

Pancreatic cancer is very common and almost uniformly fatal. Human pancreatic cancers usually have many mutations in many different genes but we know very little about how most of them drive pancreatic cancer initiation, development, and progression. Recreating these cancer-causing mutations in cells of the mouse pancreas can generate tumors that look and behave very similarly to human pancreas cancer.

Unfortunately, traditional methods used to generate mouse models of human cancer are very time-consuming and costly.

Winslow, along with postdoctoral scholar Shin-Heng Chiou, PhD, and graduate student Ian Winters, turned to the latest darling of the biochemistry world — the gene-editing system known as CRISPR — to devise a way to quickly and efficiently turn off genes implicated in the development of pancreatic cancer in laboratory mice. Their work will be featured on the cover of Genes and Development on Monday. As Winslow described:

Our goal was use CRISPR/Cas9 genome editing to make altering a gene of interest in pancreas cancer simple and fast. Shin-Heng and Ian worked together to develop novel tools and bring them together to generate this new system that we hope will dramatically accelerate our understanding of pancreas cancer. The increased basic understanding of how this cancer works may ultimately lead to better therapies for patients.

In a long list of hypotheses going back decades, researchers have tried to explain the peopling of North and South America as a series of separate waves of immigration by ancient people from Siberia. For decades, in fact, researchers have been arguing about how many distinct peoples walked over the massive, 600,000-square-mile land bridge that once connected Siberia and Alaska and, also, how many thousands of years ago each of those migrations occurred.

In the last few years, some researchers have begun to suspect that a single group of Siberians may have walked onto that land bridge and became marooned there for several thousand years before traveling the rest of the way into the Americas. But others have been holding out for a two-wave hypothesis, with a first wave of Asians from as far away as India and a later wave of people from farther north.

Today, in Science, an international team of geneticists, evolutionary biologists, and statisticians concluded that all Native Americans descended from a single immigration event out of Siberia. The team looked at the DNA from 110 modern Native Americans and 23 who died 200 to 6,000 years ago and compared their genomes to those of more than 3,000 individuals from around the world.

One of the lead authors is María Ávila-Arcos, PhD, a postdoctoral researcher in the lab of Stanford professor of genetics Carlos Bustamante, PhD. Ávila-Arcos led many of the statistical analyses for the paper, including comparison of whole human genomes from diverse Native American populations—both modern and ancient. Bustamante is also a co-author, along with Stanford professor of structural biology and of microbiology and immunology, Peter Parham, PhD, five other Stanford researchers, and dozens of researchers from around the world.

“For a long time,” Bustamante told me, “we’ve sought to understand the genetic history of the first people to populate the Americas and how they relate to modern day populations. This project brought together a large interdisciplinary team and amassed the largest data set to date on this problem. We found strong evidence for a single major wave and subsequent divergence of the founding population.”

The new genetic analysis suggests that the first immigrants to America left Siberia no more than 23,000 years ago, and then lived in isolation on the grassy plains of the Beringia land bridge for no more than 8,000 years. Those plains disappeared beneath rising seas 10,000 years ago.

Once in the Americas, ancient Native Americans split into two major lineages about 13,000 years ago. One lineage populated both North and South America and one stayed in North America.

Drop into any support group meeting, and you’ll likely find that many of the addicts there had a parent who was also an addict. It’s estimated that alcoholism (now sometimes called alcohol-use disorder) is 50 percent heritable, although researchers have struggled to identify genes specifically associated with the condition.

The hunt continues for alcohol-use disorder related genes, and a new frontier in the field is the study of the epigenome, a term that refers to inherited changes that affect gene expression, rather than the genes themselves. A new review by a team based at the University of Pittsburgh School of Medicine in the journal Alcohol compiles all that is known about the effects of the epigenome on alcohol inheritance.

“Only recently, with improvements in technology to identify epigenetic modifications in germ cells, has it been possible to identify mechanisms by which paternal ethanol (alcohol) exposure alters offspring behavior,” the researchers wrote.

The basic mechanism is that traits can be passed on through modification of the proteins associated with DNA; these proteins control how genes are expressed. Several studies have examined the role of a father’s alcohol use in the time period surrounding conception, finding their children more likely to suffer from some psychiatric disorders; in research on mice, some effects of paternal alcohol use include low birth weight and decreased grooming. These effects are likely attributed to the alteration of the development of sperm, the researchers write.

Many mysteries remain, leaving plenty of opportunities for additional research. Now, the team is starting to examine how paternal exposure affects offspring’s alcohol consumption.

“What’s my prognosis?” is a question that’s likely on the mind, and lips, of nearly every person newly diagnosed with any form of cancer. But, with a few exceptions, there’s still not a good way for clinicians to answer. Every tumor is highly individual, and it’s difficult to identify anything more than general trends with regard to the type and stage of the tumor.

Now, hematologist and oncologist Ash Alizadeh, MD, PhD; radiologist Sylvia Plevritis, PhD; postdoctoral scholar Aaron Newman, PhD; and senior research scientist Andrew Gentles, PhD, have created a database that links the gene-expression patterns of individual cancers of 39 types with the survival data of the more than 18,000 patients from whom they were isolated. The researchers hope that the resource, which they’ve termed PRECOG, for “prediction of cancer outcomes from genomic profiles” will provide a better understanding of why some cancer patients do well, and some do poorly. Their research was published today in Nature Medicine.

Researchers have tried for years to identify specific patterns of gene expression in cancerous tumors that differ from those in normal tissue. By doing so, it may be possible to learn what has gone wrong in the cancer cells, and give ideas as to how best to block the cells’ destructive growth. But the extreme variability among individual patients and tumors has made the process difficult, even when focused on particular cancer types.

Instead, the researchers pulled back and sought patterns that might become clear only when many types of cancers, and thousands of patients were lumped together for study:

Gentles and Alizadeh first collected publicly available data on gene expression patterns of many types of cancers. They then painstakingly matched the gene expression profiles with clinical information about the patients, including their age, disease status and how long they survived after diagnosis. Together with Newman, they combined the studies into a final database.

“We wanted to be able to connect gene expression data with patient outcome for thousands of people at once,” said Alizadeh. “Then we could ask what we could learn more broadly.”

The researchers found that they were able to identify key molecular pathways that could stratify survival across many cancer types:

In particular, [they] found that high expression of a gene called FOXM1, which is involved in cell growth, was associated with a poor prognosis across multiple cancers, while the expression of the KLRB1 gene, which modulates the body’s immune response to cancer, seemed to confer a protective effect.

Small cell lung cancer is one of the most deadly kinds of cancers. Typically this aggressive disease is diagnosed fairly late in its course, and the survival rates are so dismal that doctors are reluctant to even subject the patient to surgery to remove the tumor for study. As a result, little is known about the molecular causes of this type of cancer, and no new treatments have been approved by the Food and Drug Administration since 1995.

Now a massive collaboration among researchers around the world, including the University of Cologne in Germany and Stanford, has resulted in the collection of more than 100 human small cell lung cancer tumors. Researchers sequenced the genomes of the tumors and identified some key steps in their development. They also found a potential new weak link for treatment.

The findings were published today in Nature, and Stanford cancer researcher Julien Sage, PhD, one of three co-senior authors of the paper, provided some details in an email:

With this larger number of specimens analyzed, a more detailed picture of the mutations that contribute to the development of small cell lung cancer now emerges. These studies confirmed what was suspected before, that loss of function of the two tumor suppressor genes, Rb and p53, is required for tumor initiation. Importantly, these analyses also identified new therapeutic targets.

The researchers also saw that, in about 25 percent of cases, the Notch protein receptor was also mutated. This protein sits on the surface of a cell; when Notch binds, it initiates a cascade of signaling events within the cell to control its development and growth. As Sage explained:

The mutations in the Notch recepetor were indicative of loss of function, suggesting that Notch normally suppresses small cell lung cancer development. Indeed, when graduate student Jing Lim in my lab activated Notch in mice genetically engineered to develop small cell lung cancer, we found a potent suppression of tumor development. These data identify the Notch signaling pathway as a novel therapeutic target in a cancer type for which new therapies are critically needed.

This is not Sage’s first foray into fighting small cell lung cancer. In 2013, he collaborated with other researchers at Stanford, including oncologist Joel Neal, MD, PhD, to identify a class of antidepressants as a possible therapy for the disease.

I’m often humbled by my job. Well, not the job, exactly, but the physicians, researchers, and especially patients who take the time to speak with me about their goals and passions, their triumphs and fears. Their insight helps me as I struggle to interpret what goes on here at the Stanford University School of Medicine for others across the university and even around the world.

But every once in a while, an article comes along that brings me to my (emotional) knees. My article “The Butterfly Effect” in the latest issue of Stanford Medicine magazine describes the toll of a devastating skin disease called epidermoloysis bullosa on two young men and their families, as well as the determined efforts of a dedicated team of doctors and scientists to find a treatment. As a result, Stanford recently launched the world’s first stem-cell based trial aimed at correcting the faulty gene in the skin cells of patients with a severe form of the condition, which is often called EB.

I trace the path of one family as they learn, mere hours after his birth, that their son, Garrett Spaulding, has EB, which compromises the ability of the outer layers of the to stick together during friction or pressure. Patients develop large blisters and open wounds over much of their bodies. It’s incurable, fatal, and nearly indescribably painful. Paul Khavari, MD, PhD, now the chair of Stanford’s Department of Dermatology, was a young doctor at the time newborn Garrett was admitted to Lucile Packard Children’s Hospital Stanford in 1997.

“His whole body, his skin was blistered and falling off everywhere someone had touched him,” Khavari recalls in the article. “His parents were devastated, of course, at a time that was supposed to be one of the most joyful of their lives.”

Garrett’s now 18 years old, but the disease is taking its toll.

You’ll also meet Paul Martinez, one of the first participants in Stanford’s new clinical trial. He’s 32, which makes him an old man in the EB community. Unlike many EB patients, he has finished high school and completed a college degree in business marketing with a dogged determination that makes me ashamed of my petty complaints about my minor life trials. And he’s done it without relying on the pain medications essential for most EB patients. As he explains in the article:

We don’t know what it is like to not be in pain. It’s just normal for us. […] I have a very high tolerance, and don’t take any pain medication. I cherish my mind a lot. Rather than feel like a zombie, I prefer to feel the pain and feel alive.

Every year, upwards of $140 billion a year gets spent on cosmetics. In the United States alone, says an authoritative report, a recent year saw upwards of 5.6 million Botox procedures, 1.1 million chemical peels, almost a half-million laser skin procedures, 196,286 eyelid surgeries and a whole bunch of face lifts.

If you’ve got the courage to compare your present-tense face with the one you were wearing 20 or even 10 years ago, you’ll see why. As I wrote in a just-published Stanford Medicine article, “Wither youth?”:

The terrain of aging skin grows all too familiar with the passing years: bags under the eyes, crow’s feet, jowls, tiny tangles of blood vessels, ever more pronounced pores and pits and pigmentation irregularities. Then there are wrinkles — long, deep “frown lines” radiating upward from the inside edges of the eyebrows and “laugh lines” that trace a furrow from our nostrils to the edges of our lips in our 40s, and finer lines that start crisscrossing our faces in our 50s. Sagging skin gets more prominent in our later years as we lose bone and fat.

“And,” I added wistfully, “it’s all right there on the very outside of us, where everyone else can see it.”

Stanford dermatologist Anne Chang, MD, who sees a whole lot of skin, got to wondering: Why does skin grow old? Armed with a sophisticated understanding of genetics, she went beyond lamenting lost youth and resolved to address the question scientifically, asking: “Can you turn back time? Can aging effects be reversed? Can you rejuvenate skin, make it young again?”

The answers she’s come up with so far – from hereditary factors to a possible underlying genetic basis for how some treatments now in common commercial cosmetic use (such as broadband light therapy) could potentially slow or even reverse the aging of skin – are described in my magazine article.

Keynote talks and presentations from the 2015 Big Data in Biomedicine conference at Stanford are now available on the Stanford YouTube channel. To continue the discussion of how big data can be harnessed to improve the practice of medicine and enhance human health, we’re featuring a selection of the videos on Scope.

Four years ago, Matthew Might, PhD, and his wife, Christina, learned that their son Bertrand was the first person to be diagnosed with ultra-rare genetic disorder called N-Glycanase Disorder. At the 2015 Big Data in Biomedicine conference at Stanford, Might recounted the story of his son’s medical odyssey and explained how a team of Duke University researchers used whole-exome sequencing, which is a protein-focused variant of whole-genome sequencing, on himself, his wife and Bertrand to arrive at his son’s diagnosis.

Watch the video above to find out how Might and his family, who turned a deaf ear to doctors’ advice that nothing could be done for their son, harnessed the power of the Internet to identify 35 more patients with the same disorder and are now leading the charge in helping scientists better understand the disorder.